One_at_a_time (bonsai.bonsai.extra_proc.Bonsai_extra_proc.One_at_a

module Status = Bonsai_extra.One_at_a_time.Status

module Response = Bonsai_extra.One_at_a_time.Response

val effect : 
  ('query -> 'response Effect.t) Bonsai.t ->
  Bonsai.graph @ local ->
  (('query -> 'response Response.t Effect.t) * Status.t) Bonsai.t

Turns the input effect into an effect which ensures that only one instance of it is running at a time. If another instance of the effect is already running, then Busy is returned instead of running the effect. In addition, it also returns a value representing whether or not an instance of the effect is in progress.

CAREFUL: If the effect function raises while it is executing, then the status will stay at busy, since the computation is unable to witness that the effect completed.